AN ABSTRACT OF THE THESIS OF Safdar Ali for the degree of Master of Science in Soil Science presented on December 16, 1988. Title: Stability of Soil Structure for Water Movement in an Aridisol. Redacted for privacy Abstract approved: Benno P. Warkentin Lack of stability of soil aggregates for water movement is a major problem in arid soils due to low organic matter and higher sodium contents. Soil amendments for improving stability of structure and increasing infiltration of water are essential to solve water management problems in these areas. Different rates of two amendments, gypsum and polyacrylamide, were applied to determine the optimum rate needed for maximum increase in infiltration of water into soil columns under laboratory conditions. The structural stability of soil samples taken from an experimental area at the Malheur Experiment Station, Ontario, Oregon was characterized by a wet sieving method. It was found that gypsum salt applied at the rate of 25 tonnes/ha increased the infiltration. The wetting front of saturated and half saturated gypsum solutions moved faster into soil columns than that of water. The effect was due to replacing sodium from exchange sites by calcium ions. The saturated gypsum solution had equivalents of calcium that were more than double the total number of equivalents of exchangeable sodium in the entire soil column. Polyacrylamide (PAM) solution applied at 7.5, 15, and 30 ppm concentration to soil columns did not increase the rate of infiltration over the check. This was apparently due to the adsorption of PAM on soil particles. However, the wetting front of water moved faster in PAM treated aggregates than in the check without PAM treatment. The PAM was mixed with soil at rates of 120 and 240 ppm by weight and aggregates were made by pressing the PAM treated soil through a 2 mm sieve. The columns were packed with these air-dried aggregates. Furthermore, it was found that stability of PAM treated aggregates was significantly higher than of the untreated aggregates. The data analysis of the samples taken from a field trial at Malheur Experiment Station indicates that both gypsum and PAM increased the stability of soil structure over the check. STABILITY OF SOIL STRUCTURE FOR WATER MOVEMENT IN AN ARIDISOL by Safdar Ali A THESIS Submitted to Oregon State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Completed December 16, 1988 CommencementJune 1989 APPROVED: Redacted for privacy Profess of Soil Science in charge of major Redacted for privacy Head of De, rtmerd of Soil Science Redacted for privacy Dean of Gradua School (1 (7 Date thesis is presented December 16, 1988 Typed by Safdar Ali ACKNOWLEDGMENTS I wish to express my deep appreciation to my major professor Dr. Benno P. Warkentin, for the guidance, assistance and friendship which have been so valuable during my study and preparation of this thesis. Thanks and appreciation are also extended to Dr. James A. Vomocil, Dr. Floyd E. Bolton and Dr. Delbert D. Hemphill for serving on my graduate committee. I would like also to thank Dr. Clinton C. Shock for the cooperation in providing the soil samples for this study. I would like also to thank the Food and Agriculture Organization and Pakistan Agricultural Research Council for their financial support to complete this study and to continue for a doctoral program. Thanks to all members of Soil Science Department family for the help. Finally, I am deeply appreciative for the encouragement and assistance of my wife Bushra. We love our baby daughter Sana. TABLE OF CONTENTS Contents Page 1. INTRODUCTION 1 2. REVIEW OF LITERATURE 4 2.1 On Infiltration 4 2.2 On Conditioners 4 2.3 On Gypsum 8 3. MATERIALS AND METHODS 12 3.1 Soil 12 3.2 Column Preparation 12 3.3 Infiltration 13 3.3.1 Ground Gypsum 13 3.3.2 Gypsum Solution 13 3.3.3 Polyacryalamide (PAM) Solution 14 3.3.4 Polyacrylamide (PAM) Added to Soil 14 3.4 Water Stable Aggregates 14 4. RESULTS 17 4.1 Infiltration 17 4.1.1 Effect of Gypsum on Infiltration 17 4.1.1.1 Gypsum Salt, Experiment 1 17 4.1.1.2 Gypsum Salt, Experiment 2 18 4.1.1.3 Gypsum Solution 18 4.1.2 Effect of Polyacrylamide (PAM) on Infiltration 20 4.1.2.1 Polyacrylamide Solution 20 4.1.2.2 Polyacrylamide Mixed with Soil 21 TABLE OF CONTENTS (continued) Page 4.2 Soil Aggregate Stability 22 4.2.1 Effect of PAM on Soil Aggregate Stability ( Samples prepared in the laboratory) 22 4.2.2 Effect of Soil Amendments on Aggregate Stability, Field Samples 23 5. DISCUSSION 32 5.1 On Infiltration 32 5.1.1 Effect of Gypsum 32 5.1.2 Effect of Polyacrylamide (PAM) 33 5.2 On Stability of Aggregates 35 6. SUMMARY AND CONCLUSION 37 6.1 Summary 37 6.2 Conclusions 39 7. REFERENCES 40 8. APPENDIX 46 LIST OF FIGURES Figure Page 1. Effect of Solid Gypsum Mixed with Soil on 24 Infiltration (large columns). 2. Effect of Gypsum Mixed with Soil on Water 25 Infiltration (small columns). 3. Effect of Gypsum Mixed with Soil on Water 26 Infiltration (omitted l& 2% gypsum). 4. Effect of Gypsum Solution on Infiltration 27 (large columns, saturation conc. not known). 5. Effect of Gypsum Solution on Infiltration 28 (small columns, concentration measured) 6. Effect of PAM Solution on Infiltration 29 (Average of duplicate determinations). 7. Effect of PAM Mixed with Soil on Infiltration 30 (Average of duplicate determinations). 8. Infiltration Comparison of Check Samples. 31 LIST OF APPENDIX TABLES Table Page Al. Physico-chemical Analysis of the Soil Samples. 47 A2. Effect of Gypsum Salt Mixed with Soil on 48 Infiltration. A3. Effect of Gypsum Salt Mixed with Soil on 49 Infiltration. A4. Effect of Gypsum Solution on Infiltration 50 (Average of duplicate determinations). A5. Effect of Gypsum Solution on Infiltration. 51 A6. Effect of Gypsum Solution on Infiltration 52 (small columns). A7. Effect of PAM Solution on Infiltration 54 (Average of duplicate determinations). A8. Effect of PAM Solution on Infiltration. 55 A9. Effect of PAM Mixed with Soil on Infiltration 56 (Average of duplicate determinations). A10. Effect of PAM Mixed with Soil on Infiltration. 57 All. Effect of PAM on Aggregate Stability (%) 58 (Samples prepared in the laboratory). Al2. Effect of Soil Amendments on Stability of 59 Aggregates Sampled in the Field. Al3 Depth of Wetting. Regression equation of best 61 fit line for plots of accumulative time (hours) vs square root infiltration(cm). LIST OF TABLES Table Page Al. Physico-chemical Analysis of the Soil Samples. 47 A2. Effect of Gypsum Salt Mixed with Soil on 48 Infiltration. A3. Effect of Gypsum Salt Mixed with Soil on 49 Infiltration. A4. Effect of Gypsum Solution on Infiltration 50 (Average of duplicate determinations). A5. Effect of Gypsum Solution on Infiltration. 51 A6. Effect of Gypsum Solution on Infiltration 52 (small columns). A7. Effect of PAM Solution on Infiltration 54 (Average of duplicate determinations). A8. Effect of PAM Solution on Infiltration. 55 A9. Effect of PAM Mixed with Soil on Infiltration 56 (Average of duplicate determinations). A10. Effect of PAM Mixed with Soil on Infiltration. 57 All. Effect of PAM on Aggregate Stability (%) 58 (Samples prepared in the laboratory). Al2. Effect of Soil Amendments on Stability of 59 Aggregates Sampled in the Field. A13 Depth of Wetting. Regression equation of best 61 fit line for plots of accumulative time (hours) vs square root infiltration(cm). STABILITY OF SOIL STRUCTURE FOR WATER MOVEMENT IN AN ARIDISOL 1. INTRODUCTION The Treasure Valley in Eastern Oregon has an agricultural resource-based economy. Economic development of this economy involves stimulating the production of high value crops and increasing the number of industries that process agricultural raw materials. Industry converts farm products into higher value forms, thus providing income and employment. The potato has high productivity and can provide an adequate return per acre. The potato has been successfully industrialized in the Treasure Valley. The major industrialized product is frozen french fried potatoes. In the fall of 1985, the potato harvest presented processors with a problem of crisis proportions. Potato quality was insufficient to satisfy processors because of an internal defect called "sugar-end" or "dark end". A sugar-end potato from this region typically has more sugar in the stem end than in the rest of the potato. When the potato strips are fried at 375 Fo for a 2.5 minutes, the end with the greater sugars, the part of the potato strip near the stem end of the potato, develops a dark color which is 2 unacceptable for the fast food industry. There is reason to believe that "sugar-end" is associated with the development of water stress in the potato plant or potato tuber. It is further believed that this water stress may arise because of difficulties in managing water for good irrigation of the root zone in some potato fields. The soils of the Treasure Valley are high in silt, low in clay, and low in organic matter; therefore, the infiltration of water into these soils is relatively slow. This slow water infiltration can have the consequence of causing great differences in the amount of water which infiltrates into the soil in various parts of the field. In some parts there may be large excesses of water, while in other parts there may be deficiencies. Under such conditions, it is difficult to continue to get good irrigations, putting the right amount of water at the right place at the right time for the full period of the potato crop season.